A piezoelectric converter comprising a piezoelectric actuator that includes a piezoelectric ceramic layer of thin plate shape being stacked on the surface of a substrate on the side thereof whereon cavities to be filled with a liquid are formed wherein, in order to prevent a significant buckling deformation from occurring in a region of the piezoelectric actuator that corresponds to the cavities of the substrate, the thickness T (mm) of the piezoelectric ceramic layer and maximum width W (mm) of the cavities in the direction of substrate surface are set so as to satisfy the relation of expression (1). T.gtoreq.(19.6 W+5.5).times.10.sup.-3 (1)